Various types of objects, such as videos, widgets, applications, etc., propagate through social networks. For example, a person may install a video on his or her web site. Other people may then see the video and decide to install it on their own web sites. There may be an initial user, or group of users, who download the object without having seen a copy of the object. These users may have learned about the object from an original source, such as from the object's creator or through a publicity campaign. However, once that initial group has downloaded the object and has installed instances of the object where others can see it (e.g., on a web site), the object propagates when one user sees the object and is thereby encouraged to obtain a copy for himself or herself.
Some types of objects propagate by referring an interested entity to a server that provides and/or installs a copy of the object. For example, a widget might provide a link that allows a user to get a copy of the widget. Thus, if a person sees the widget on a web site and is interested in obtaining the widget for his or her own site, the person could click the link. The link would contact the server and set in motion the process of providing and/or installing the widget. In this sense, certain objects propagate by way of referrals: one instance of an object makes a referral, which results in another instance of the object being obtained.
The fact that an object has propagated through referrals provides clues about how objects move through a social network. For example, objects may initially be promoted through some sort of publicity effort, and then may propagate from person to person through a chain of referrals. It may be of interest to know how many instances of the object are downloaded as a result of the initial publicity effort, and how many instances are downloaded as a result of referrals. Moreover, it may be of interest to know how long a chain of referrals is. For example, the fact that an object was downloaded through a chain of referrals that passed through, say, fifteen people may suggest that the object, or its initial publicity campaign, are particularly effective at encouraging propagation. However, objects and the systems in which they are distributed typically do not support the marshaling and analysis of this type of information.